1. Field of the Invention
This invention relates generally to communication systems, and, more particularly, to wireless communication systems.
2. Description of the Related Art
Conventional wireless communication systems typically include a plurality of base stations (e.g., Node Bs) that provide wireless connectivity over a corresponding plurality of geographic areas or cells. Mobile units within the area serviced by the base stations may access the system by establishing a wireless communication link with one of the base stations. Typically, each mobile unit maintains communications with the system as it passes through an area by communicating with a series of base stations that provide wireless connectivity to the cells that are visited by the mobile unit. The mobile unit may communicate with the closest base station, the base station with the strongest signal, the base station with a capacity sufficient to accept communications, or some combination of base stations selected according to these handoff rules or other handoff rules. Communications between the mobile unit and the base station are wireless and are often referred to as taking place over the air interface.
Communications between the mobile units and the base stations may include voice and/or high-speed data. High speed wireless data systems such as Evolution-Data Optimized (EVDO Rev.A), Universal Mobile Telecommunications System (UMTS), High-Speed Downlink Packet Access (HSDPA), E-DCH and Evolution Data and Voice (EVDV) have significantly improved the air interface channel data rates to support various packet data services that require high-speed channels. In addition, multiple standards are defined to efficiently support applications that require large-data transfers, such as continuously running data flows for broadcast or multicast over the air interface. However, support for fast and flexible transmissions of short messages or data information to a group of users (active or idle) is lacking in all existing 3G air interface standards. Current standards only specify how to handle data flows and streaming applications. There is no per-message multicast capability in existing cellular wireless standards. Instead, short messages are sent to individual users using a unicast method. The process involves locating users, setting up traffic channels and sending the message over each traffic channel using unicast messages. Sending the same short message to multiple users through unicast process incurs longer delays and inefficient use of the air interface and system resources.
One example of a technique for locating users and then transmitting unicast messages to these users is known as quick paging of idle mobile units. In quick paging, each idle mobile unit periodically wakes up during a predetermined portion of a paging or wake-up cycle. When the idle mobile unit wakes up during the predetermined portion of the wake-up cycle, it attempts to detect a quick paging message that indicates that a paging message is going to be unicast to this mobile unit during a subsequent portion of the wake-up cycle. The different mobile units are assigned to different portions of the wake-up cycle so that they do not inadvertently detect a paging message that is directed to a different mobile unit. For example, different mobile units may be assigned different offsets within the wake-up cycle. Thus, quick paging messages and unicast paging messages destined for different mobile units can be distinguished by transmitting them in the different portions of the wake-up cycle assigned to the different mobile units.
FIG. 1 shows a conventional time sequence 100 of successive control cycles 105 that form a wake-up cycle 110. Each wake-up cycle 110 in FIG. 1 includes 12 control cycles 105 and each control cycle 105 comprises 256 slots. An idle mobile unit may wake up during the first control cycle 105 (labeled with “1”) of each wake-up cycle 110 and attempt to decode a quick page that has been transmitted by a base station. If the idle mobile unit detects a quick page, which indicates that a unicast paging message is going to be transmitted to the mobile unit, then it may remain awake for the subsequent control cycle 105 (labeled with “2”) and attempt to decode the unicast paging message. Other idle mobile units may be assigned to other control cycles 105 and may therefore monitor these control cycles 105 to detect quick pages that are directed to these mobile units. For example, another idle mobile unit may wake up during the sixth control cycle 105 (labeled with “6”) of each wake-up cycle 110 and attempt to decode a quick page that has been transmitted by a base station. If the idle mobile unit detects a quick page, which indicates that a unicast paging message is going to be transmitted to the mobile unit, then it may remain awake for the subsequent control cycle 105 (labeled with “7”) and attempt to decode the unicast paging message.